OK, after some ordering difficulty I finally got the climate control cable in. I promptly took it apart and snapped photos. The part number is #10418042 and it is about 20 bucks from GM Parts Direct.
There is a small end that attaches to the knob and a big end that goes under the dash on the passenger side. Just drop the plastic foot panel under the dash and follow the cable. It is held on with on screw.
The sheath holds one long cable that has the ends crimped with lugs on the big end and a crimp in the center so the knob can grab it. The whole cable is under tension from the spring on the big end. The sheath is also divided in two to keep the 2 cables from rubbing against one another. I doubt that makes any difference and a single large holes should work just as well. How much rubbing do they actually see anyway?
I think I have a good plan of attack to lengthen this cable as my old idea won't work. I'll leave that for the end.
Here is the back of the controls.